Valve-drive components according to this general type are known in the state of the art as effective means for targeted optimization of the fuel consumption, power behavior, and exhaust-gas emissions of internal combustion engines. Such valve-drive components typically have coupling elements, which can be displaced depending on the operating point and with which the transmission elements of the valve-drive components can be connected with a positive fit in the transmission direction.
To be included here is the switchable cam follower arranged in the flow of forces between a camshaft of the internal combustion engine and the gas-exchange valves. With this cam follower, discrete cam projections tuned to the operating state of the internal combustion engine can be transferred selectively to a gas-exchange valve or can be completely canceled out for making the gas-exchange valve stationary. A good overview of switchable cam followers can be obtained by someone skilled in the art with, for example, the manual “Verbrennungsmotor” [“Internal Combustion Engine”], first edition published in April 2002 by Vieweg-Verlag. There, in Chapter 10.4.2, Page 357 and on, systems configured for sequential use are described with step-wise stroke and opening period duration of the gas-exchange valve. Switchable finger levers and rocker arms, as well as a switchable cup tappets, which provide hydraulically activated coupling elements for locking the transmission elements and which are used for switching or deactivating the gas-exchange valves. Furthermore, a switchable rocker arm in WO 2004/094791 and also a switchable roller tappet in DE 102 04 673 A1 for a tappet push-rod valve drive—both with hydraulically activated coupling elements—are proposed. Finally, a switchable cam follower is understood by someone skilled in the art to be a support element supported statically in the internal combustion engine, as proposed, for example, in DE 44 04 145 A1.
Furthermore, camshaft adjusters, which change the control times of gas-exchange valves and which have one or more coupling elements for locking a stator as a drive-side transmission element to a rotor as a driven-side transmission element, also belong to the valve-drive components according to this class. For hydraulically activated camshaft adjusters, such a coupling element maintains the control times necessary for the starting process of the internal combustion engine as a priority, because in this operating state, there is still not sufficient hydraulic means pressure for powering the camshaft adjuster. Additional details and configurations are described, for example, in the book “Nockenwellenverstellungen für Ottomotoren”[ “Camshaft adjustments for Otto engines”] on Page 44 and on. This book was published in the year 2002 by Verlag Moderne Industrie.
Finally, switchable camshafts are to be named, which provide cams with cam segments that can be adjusted relative to each other and that can be locked by means of coupling elements as transmission elements. Such a camshaft follows from, among other things, WO 2004/109068 A1.
All of the mentioned valve-drive components are based on the principle of connecting their transmission elements with a positive fit by coupling elements that can be displaced as a function of the operating point in the transmission direction. In reference to trouble-free functioning of the switchable valve-drive components over the service life of the internal combustion engine, the design of the coupling elements and their contact partners in the transmission elements are of the highest importance. Here, an essential objective is long-term smooth-running displacement of the coupling elements as a prerequisite for its reproducible switching process, which should also end within a cam base circle phase for switchable cam followers or switchable camshafts even at very high rpms and/or for a cold internal combustion engine with high-viscosity lubricating oil. For this purpose, hydraulically activated coupling elements are typically guided with a tight clearance fit, in order to generate a quick pressure build-up in front of the coupling elements, wherein due to the tight clearance fit, a minimal and minimally dispersive mechanical play can be simultaneously guaranteed within the switchable valve drive components. Because the opening course of the gas-exchange valves is changed relative to the associated cam projection by the mechanical play, another objective is to hold the mechanical play and its dispersion, especially for switchable cam followers, as constant as possible over the service life of the internal combustion engine, in order to generate the most uniform and constant opening courses of all of the gas-exchange valves of the internal combustion engine as possible. This is a prerequisite for long-term good idle running quality for the internal combustion engine, which reacts sensitively to changes of the control times of simultaneously opened inlet and outlet valves, especially at this operating point.
An essential prerequisite for the long-term smooth-running displacement and also the most constant mechanical play of the coupling elements as possible is the form and surface stability of the coupling elements and their contact partners in the transmission elements. In this respect, even very high surface loads may not lead to significant deformation or significant wear on the loaded surfaces. These surface stresses result initially from material stresses in the region of Hertzian stress contacts or in the region of edge carriers, which appear between coupling elements and transmission elements, for example, in the region of the parting lines between the transmission elements stressed by the coupling elements. Furthermore, dynamic loading of the coupling elements clamped between the transmission elements leads to mutual micro-movements of the involved surfaces, which results in a considerable risk of impermissibly high adhesive and/or abrasive wear for a lack of lubricating oil film and/or for a comparatively high content of abrasive particles in the lubricating oil. These particles can be, for example, soot particles as products of an incomplete combustion in the internal combustion engine, which leads via so-called blow-by into the crankcase and thus via the lubricating oil to the coupling elements.
Especially dynamic highly stressed switchable valve-drive components, such as, for example, cam followers with comparatively large moving mass, are exposed to this risk of wear and tear. To be counted here are primarily switchable roller tappets for tappet push-rod valve drives or also switchable finger levers, which can lead to impermissibly high wear and the progression of wear of the coupling elements and their contact partners in the transmission elements during the operation of the internal combustion engine. From the relevant state of the art cited as an example above, however, no means are known to the applicant for overcoming this problem under consideration of manufacturing and cost aspects of a large-series production.